I was asked to fix a machine affected by this after upgrading from trusty to xenial (LTS releases).
On this machine systemctl start sddm started sddm successfully, but enable did nothing.
Reinstalling the sddm package added the previously missing /etc/systems/system/display-manager.service symlink, which fixed the issue.
I was asked to fix a machine affected by this after upgrading from trusty to xenial (LTS releases).
On this machine systemctl start sddm started sddm successfully, but enable did nothing.
Reinstalling the sddm package added the previously missing /etc/systems/ system/ display- manager. service symlink, which fixed the issue.